Renal cell function requires the maintenance of polarized plasma membrane domains with distinct protein and lipid compositions. This is accomplished in part by the targeted delivery of newly synthesized and recycling membrane proteins to the apical or basolateral surface. Apical sorting signals are extraordinarily diverse and include peptide-, lipid- and glycan-dependent motifs. Interestingly, recent data from our and other laboratories suggest that apical proteins with different targeting signals traffic to the surface in distinct populations of transport carriers. These post-Golgi carriers may traffic directly to the cell surface;however, recent studies suggest that some newly-synthesized proteins transit recycling endosomes en route to the cell surface. Our long term goals are to identify the signals that direct apical delivery of newly- synthesized proteins, and to understand how these signals are interpreted at various stages along the biosynthetic and postendocytic pathways. The aims of this proposal are to identify proteins that regulate distinct pathways to the apical surface in renal epithelial cells, to assess the role of endocytic compartments in the polarized biosynthetic traffic of different classes of apical proteins, and to dissect the mechanism of glycan-dependent sorting along the biosynthetic and postendocytic pathways. The results of our studies will refine our understanding of how transport cues on physiologically relevant molecules are interpreted at distinct intracellular sites to enable proper sorting. PROJECT NARRATIVE The primary function of the kidney is the reabsorption of water, ions, and metabolites from the forming urine to the bloodstream. The surfaces of kidney cells are subdivided into different domains that face the urine and bloodstream and which contain distinct proteins and lipids;and this asymmetric distribution of surface components is essential for proper kidney function. Our goal is to understand how kidney cells create and maintain these distinct surface domains. The results of our research will provide critical basic information that can be applied to the design of potential therapies to combat kidney-related diseases including renal carcinoma, acute renal failure, and hypertension.